In some radio communication systems, radio frequency (RF) signals are communicated between a plurality of radios and a base. Some systems are configured to support communications with “half-duplex radios” (i.e., radios that are adapted to operate in a half-duplex mode). Such systems also may be configured to support communications with “full-duplex radios” (i.e., radios that are adapted to operate in a full-duplex mode). A radio operating in half-duplex mode may either receive RF signals or transmit RF signals, but not both simultaneously. In contrast, a radio operating in full-duplex mode may transmit and receive RF signals simultaneously using different frequencies. Although full-duplex radios have certain advantages over half-duplex radios, full-duplex radios are not without disadvantages. For example, full-duplex radios tend to have significantly greater hardware complexity than half-duplex radios. Therefore, full-duplex radios generally are more expensive than half-duplex radios. In addition, because full-duplex radios transmit and receive information using different frequencies, full-duplex radios tend to consume more available system bandwidth than half-duplex radios.
Half-duplex radios may be used in a time division duplex (TDD) system, which is a communication system in which time division multiplexing is used to separate transmit and receive RF signals. A half-duplex radio adapted for use within a TDD system may include a relatively simple switch between the radio's transmit and receive subsystems. The switch is operable to cause the radio either to receive RF signals from a base or to transmit RF signals to the base, but not both simultaneously. A half-duplex radio and a base in a TDD system use a single frequency for transmitting and receiving. Therefore, communications between the half-duplex radio and the base may consume less available bandwidth than a full-duplex system. Using TDD, the base transmits while the radio is receiving, and vice versa. During any given time interval, only the base or the half-duplex radio may be transmitting, while the other device is receiving. However, when propagation delays between the radio and the base become too long (e.g., when the length of a communication frame is relatively short compared with the propagation delay), a half-duplex radio is incapable of maintaining this switching synchronicity with the base. Accordingly, communications with half-duplex radios is not generally supported in TDD communication systems in which long propagation delays are inherent.
Because of the advantages of half-duplex radios, however, methods and apparatus are desired to support communications with half-duplex radios in TDD communication systems having inherently long propagation delays. Accordingly, what are needed are methods and apparatus for providing half-duplex communications in a radio communication system, and more particularly in a TDD radio communication system, and even more particularly in a TDD radio communication system in which long propagation delays may exist between a radio and a base. Other features and characteristics of the inventive subject matter will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and this background.